Potentiometric and spectroscopic (UV-Vis, CD and EPR) studies were carried out on copper(II) complexes with chicken prion protein N-terminal fragments, Ac-(PHNPGY)(4)-NH(2), and the mutated residue, Ac-(PHNPGF)(4)-NH(2), to assess the role of tyrosine in the copper coordination. Both thermodynamic and spectroscopic results indicate that chicken prion fragments are not able to bind more than two copper ions and only with the involvement of side chain tyrosine groups. The prevailing complex shows one copper ion bound to four imidazole nitrogen atoms in the 1:1 metal to ligand ratio systems. The superoxide dismutase (SOD)-like activity of copper(II) complexes with the avian peptides and mammal analogue, Ac-(PHGGGWGQ)(4)-NH(2), was also investigated by means of Pulse radiolysis. The copper(II) complexes with avian peptides do not display SOD-like activity, while very low activity has been detected for the copper(II) complexes with mammalian tetraoctarepeat.